The groundwater map is based on 40,000 groundwater models comprising data from nearly a million watersheds.
Their findings, published in the journal Nature Geoscience, suggest the planet holds 23 million cubic kilometers of total groundwater — roughly 5.5 million cubic miles. Only six percent of that water will be replenished over the next fifty years. In other words, most of Earth's hidden groundwater reserves are nonrenewable.
Snowpacks are a vital source of water for humans, but they may shrink in some regions as the climate warms. A new study estimates how changes in showfall will affect water supplies. They found that 97 basins, currently serving two billion people, depend heavily on snowmelt. The scientists calculated that the likelihood the basins would receive less snow in the coming century was 67 percent.